Solid tumors will not grow beyond 3 - 4 mm in diameter without building up their own blood supply. Due to the essential role of tumor angiogenesis, anti-angiogenesis, mono-therapy or in- combination with other therapeutic agents, represents a very promising approach for cancer treatments. Great successes have been achieved, such as Avastin, a FDA approved anti- angiogenesis drug. However, clinical studies revealed that the cancer patient survival benefits of antiangiogenic drugs have thus far been insignificant. In addition, most current studies in development of anti-angiogenesis agent have been mainly focused on strategies of blocking VEGF/VEGFR signaling. Many agents that are developed against the VEGF/VEGFR pathway often cause unwanted biologic side effects. There is urgent need to develop anti-angiogenesis agents by targeting many other biological pathways that are involved in both stimulation and inhibition of cancer angiogenesis. We have developed a new class of anti-angiogenesis proteins by integrin ?v?3 at a novel site, the large pocket formed by the I-domain of ?v and the PSI domain of ?3. Computational modeling demonstrated that the domain 1 of rat CD2 and human CD2 spatially fit into the designed site very well. Mutations introduced at the D1-CD2 to bridge several key contacts between designed protein and the integrins optimize the binding of the designed protein with integrin. The designed proteins exhibit strong in vitro activity in induction of apoptosis on endothelial HUVEC cells with no effects on other cells. Tests with tumor nude mice PC-3 xenografts show that the designed proteins strongly inhibit tumor growth. Parallel analyses suggested that our developed protein anti-angiogenesis agents are significantly more effective than Avastin in inhibiting tumor growth. In this proposed research project, we propose experiments to further verify whether the designed protein indeed interact with integrin at the designed site, and whether the designed protein indeed exert its activity by targeting the integrin. We will extensively test the effectiveness of the developed protein anti-angiogenesis agents by various animal models of human cancers. We also design experiments to test whether our developed anti-angiogenesis proteins will have great potency for cancer treatment in combination with other anti-cancer drugs. To facilitate potential future clinical applications, we propose experiments to extensively characterize toxicity and bio-distribution of the protein agents. Our study will lead to development of a new and more effective anti-angigenesis agent for cancer treatment.